This invention relates to porous fiber burners made with metal fibers without sintering. More particularly, the invention combines ceramic fibers with metal fibers and binds the mixed fibers using the technique and binding agents that are used in the production of ceramic fiber burners. The novel mixed fiber burners of this invention have improved radiant efficiency and lowered emissions of nitrogen oxides (NO.sub.x).
Two types of porous fiber burners have been developed and are available in commerce. Sintered metal fiber burners are described in U.S. Pat. No. 4,597,734 (McCausland et al) and European Patent Application (Publication No. 0 390 255). Ceramic fiber burners have been disclosed in many patents including U.S. Pat. Nos. 3,179,156 (Weiss et al), 3,383,159 (Smith) and 4,746,287 (Lannutti).
Sintered metal fiber burners are more expensive than ceramic fiber burners and this cost difference limits their use. Moreover, the aforesaid European Patent Application discloses that large temperature fluctuations can lead to the formation of cracks or craters in the combustion surface of metal fiber burners.
The basic ceramic fiber burner as early developed by Weiss et al required improvement and the Smith and Lannutti patents contributed additives that yield definite improvement. However, the sintered metal fiber burner has better emissivity than the Weiss et al burner even as improved by Smith or Lannutti.
Accordingly, a principal object of this invention is to provide a porous fiber burner that reduces the cost of a metal fiber burner while substantially eliminating its tendency to crack and form craters.
Another important object is to provide a burner of mixed metal and ceramic fibers by utilizing the highly developed technology and existing facilities for producing ceramic fiber burners.
Other features and advantages of the invention will be apparent from the description which follows.